In the past granting period, we learned that a fundamental mechanism of aging is conserved from yeast to animals. Thus, yeast is a valuable model for at least some important aspects of aging in higher organisms. A specific gene, SIR2, is conserved in organisms from bacteria to humans. This gene clearly regulates aging by promoting longevity in yeast and C. elegans, suggesting that its effects will prove to be general. The activity of Sir2p is to deacetylate proteins when provided with co- substrate, NAD (nicotinamide-adenaline dinucleotide). Our studies in yeast indicate that the replicative aging of mother cells can be extended by calorie restriction, and that this extension requires Sir2p. Since calorie restriction is the only intervention known to extend life span in mammals, these findings may have broad implications. We have further learned that the known effects of Sir2p on genomic silencing are pertinent to yeast aging. In the next period we propose to study the mechanism of Sir2p-mediated silencing in greater detail by analyzing sir2 mutations genetically and biochemically. We further propose to use a combination of yeast genetic and molecular approaches to define the specific metabolic mechanism by which calorie restriction extends life span and how this might relate to Sir2p. In addition, we will probe the intriguing link between sojourns in stationary phase and yeast replicative aging. This particular study might provide a conceptual link between the aging of dividing and post-mitotic cells. Finally, we will began an analysis of two new genes, SSD1 and MPT5, that affect yeast aging in a SIR-2 independent way. These experiments will add to a substantial base of knowledge of aging in the simple budding yeast and will be a platform for studies of aging in higher organisms, including mammals.